Conductive Polymer - History

History

There are multiple reviews of the history of conducting polymers. The first report on polyaniline goes back to the discovery of aniline. In the mid-19th century, Henry Letheby reported the electrochemical and chemical oxidation products of aniline in acidic media, noting that reduced form was colourless but the oxidized forms were deep blue. In the early 20th century, German chemists named several compounds "aniline black" and "pyrrole black" and used them industrially. The structure was believed to be linear and octameric. In the late 1960s, Buvet proposed polyaniline devices.

The first highly-conductive organic compounds were the charge transfer complexes. In the 1950s, researchers reported that polycyclic aromatic compounds formed semi-conducting charge-transfer complex salts with halogens. In 1954, researchers at Bell Labs and elsewhere reported organic charge transfer complexes with resistivities as low as 8 ohms-cm. In the early 1970s, salts of tetrathiafulvalene were shown to exhibit almost metallic conductivity, while superconductivity was demonstrated in 1980. Broad research on charge transfer salts continues today. While these compounds were technically not polymers, this indicated that organic compounds can carry current. While organic conductors were previously intermittently discussed, the field was particularly energized by the prediction of superconductivity following the discovery of BCS theory.

In 1963 Australians Bolto, DE Weiss, and coworkers reported iodine-doped oxidized polypyrrole blacks with resistivities as low as 1 ohm·cm. This Australian group eventually claimed to reach resistivities as low as 0.03 ohm·cm with other conductive organic polymers. This resistivity is roughly equivalent to present-day efforts. The 1964 monograph Organic Semiconductors cites multiple reports of similar high-conductivity oxidized polyacetylenes. With the notable exception of charge transfer complexes (some of which are even superconductors), organic molecules were previously considered insulators or at best weakly conducting semiconductors. Subsequently, DeSurville and coworkers reported high conductivity in a polyaniline. Likewise, in 1980, Diaz and Logan reported films of polyaniline that can serve as electrodes.

Much early work on the physics and chemistry of conductive polymers was focussed on melanins, due to their biological and medical importance. For example, in the 1960s Blois et al. showed semiconduction in melanins, as well as further defining their physical structures and properties Nicolaus et al. studied the structure of melanins in detail. In 1974, while studying the role of melanin in cancer, John McGinness and coworkers described the "first experimental demonstration of an operating molecular electronic device that functions along the lines of the biopolymer conduction ideas of Szent-Gyorgi", a voltage-controlled bistable switch.

While mostly operating in the quantum realm of less than 100 nanometers, "molecular" electronic processes can collectively manifest on a macro scale. Examples include quantum tunneling, negative resistance, phonon-assisted hopping and polarons. Macro-scale active organic electronic devices were described decades before molecular-scale ones. In 1977, Alan J. Heeger, Alan MacDiarmid and Hideki Shirakawa reported similar high conductivity in oxidized iodine-doped polyacetylene. For this research, they were awarded the 2000 Nobel Prize in Chemistry "for the discovery and development of conductive polymers." Polyacetylene itself did not find practical applications, but drew the attention of scientists and encouraged the rapid growth of the field. Since the late 1980s, organic light-emitting diodes (OLEDs) have emerged as an important application of conducting polymers.